Field of the Invention
The present invention relates to a variable valve control system, and more particularly, to an engine system including a variable valve control system operated without an oil control valve causing a complicated hydraulic circuit.
Description of Related Art
In general, a variable valve control system includes a variable valve mechanism that includes a cylinder deactivation (hereinafter, referred to as “CDA”) device and a variable valve lift (hereinafter, referred to as “VVL”) device or includes a CDA or VVL device, an oil control circuit configured to supply an oil pressure, and an oil control valve (hereinafter, referred to as “OCV”) for controlling the supply of the oil pressure.
Accordingly, the variable valve control system may perform individual control or integrated control of CDA and VVL for a further improvement in fuel efficiency by controlling the latching operation (i.e., latching ON) or unlatching operation (i.e., latching OFF) of a latching pin in a variable stage manner including first, second and third stages (e.g., zero, normal, and high), according to the control of the OCV.
As a result, the variable valve control system may operate an engine in various engine control modes and be used for various engine systems.
By way of example, a four-cylinder engine may be operated in engine control modes including an engine control mode 1 in which four-cylinder combustion is performed by single lift control of intake and exhaust valves, an engine control mode 2 in which two-cylinder combustion is performed by single lift control of intake and exhaust valves and two-cylinder deactivation is performed by 0 (zero) lift control of intake and exhaust, an engine control mode 3 in which four-cylinder combustion is performed by two-stage lift control of an intake valve and single lift control of an exhaust valve, an engine control mode 4 in which two-cylinder deactivation is performed by 0 (zero) lift control of intake and exhaust, and an engine control mode 5 in which four-cylinder deactivation is performed by 0 (zero) lift control of intake and exhaust.
Furthermore, the four-cylinder engine may be operated by engine systems including a first-type engine system that enables realization of the engine control modes 1 and 2, a second-type engine system that enables realization of the engine control modes 1, 2, 3, and 4, and a third-type engine system that enables realization of the engine control modes 1, 2, 3, 4 and 5.
Thus, the variable valve control system significantly contributes to an improvement in fuel efficiency by controlling various valves for each driving region while increasing marketability by various engine systems and engine control modes.
However, the variable valve control system requires the OCV to control an oil pressure for each of the engine control modes 1, 2, 3, 4 and 5.
By way of example, the oil control circuit of the variable valve control system includes a main gallery, a control gallery, a drain hole, an OCV, an orifice, and a relief valve.
The main gallery functions as an oil line which is directly connected to a block or a head from an oil pump. The control gallery functions as an oil line that connects an outlet end portion of the OCV to a latching pin of a variable valve lift device.
When the pressure in the control gallery is higher than a relief spring force, a relief valve is opened so that oil is discharged through the drain hole to lower the pressure. The OCV includes a solenoid, a pintle, a check ball, spring, etc., and is located between the main gallery and the control gallery. The pintle pushes the check ball in the OCV when the OCV is turned on, with the consequence that the passages in the main gallery and control gallery are opened while the relief valve is pressed against a relief valve seat to block the passage between the control gallery and the drain hole, preventing oil from leaking from the control gallery.
On the other hand, the pintle is returned to an original position thereof and the check ball moves upward in the OCV when the OCV is turned off, with the consequence that the passages in the main gallery and control gallery are blocked while the pintle is lifted from the relief valve so that a gap is formed therebetween, in which case the relief valve spring serves to restrict movement of the relief valve. The orifice is located between the main gallery and the control gallery and serves to supply oil such that the control gallery is continuously filled with oil. The relief valve is opened when the differential pressure between a drain line and the control gallery is larger than a mounting load of the relief spring, and the relief valve is closed when the differential pressure is less than the mounting load. Thus, the relief valve functions to uniformly maintain the differential pressure between the drain line and the control gallery when the OCV is turned off.
Therefore, the number of OCVs is increased as the number of engine control modes is increased, causing an increase in the number of parts including main galleries, control galleries, drain holes, orifices, and relief valves, and thus leading to complexity of the oil control circuit.
For the present reason, the variable valve control system, which is applied to the third-type engine system that realizes the engine control modes 1, 2, 3, 4 and 5, may require a complicated oil control circuit with a large number of OCVs, which may lead to a loss of product competitiveness due to an increase in price and investment cost.
Moreover, the variable valve control system should be necessarily used to realize an optimal valve mode for each driving region. Hence, when both of half cylinder deactivation (or overall cylinder deactivation) and VVL are applied to one engine, there may be a problem relating to engine system packaging due to an increase in the number of components, and at the same time, a problem relating to an increase in cost.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and may not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.